A method providing precise reproducibility of magnification of electron micrographs

Reproducibility of magnification within 2 % can be achieved by photographing a diffraction grating replica at each magnification, printing these negatives at standard print magnifications, and thereafter bringing standard negatives to register with standard prints. This method was checked by removing the grid, relocating and rephotographing the same area after 2 weeks, filament change, inversion of grid, and change of accelerating voltage. When printed without changing the enlarger, all prints registered within 2%. This precision may be due to modern lenses, thinner grids, and measuring final prints of the same area of the carbon replica. This method may be used for control of magnification with any accepted standard. To facilitate measurements of specimens, magnification is expressed as Å/mm on the print, and standard print magnifications are suggested.